1. Field of the Invention
This invention relates to ribbon cartridges, such as used in typewriters, printers and the like.
2. Description of Prior Art
Prior cartridges of the type described comprise a ribbon wound on a supply spool which is wound up on a take up spool which is rotated by a driving roller according to desired printing operation. The take up spool, of such known ribbon cartridges, is adapted to be driven by the driving roller so that the take up spool will wind the ribbon by a fixed length during each printing operation. However, disadvantageously, the ribbon is often loosened or excessively tightened between the supply spool and the take up spool due to variations in tension applied to the ribbon. Thus, it is difficult to wind the ribbon by a precise predetermined length during each printing operation.
According to a known method of stabilizing the tension of the ribbon supplied by a supply spool, the ribbon, wound on the supply spool, is pressed against the inside wall surface of the cartridge by a spring member, to apply frictional resistance of the wall surface of the ribbon. This method, however, is unsatisfactory because it is difficult to apply an appropriate frictional resistance at all times to the ribbon.
Thus, with prior art devices, it is difficult to attain reliable, constant and precise amount of tension at all times.